<template>
  <Scroll class="listview" :data="data" ref="listview" :listenScroll="listenScroll" @scroll="scroll" :probeType="3">
    <ul>
      <li v-for="(group,index) in data" :key="index" class="list-group" ref="listGroup">
        <h2 class="list-group-title">{{group.title}}</h2>
        <ul>
          <li @click="selectItem(item)" v-for="item in group.item" :key="item.id" class="list-group-item">
            <img class="avatar" v-lazy="item.avatar" />
            <span class="name">{{item.name}}</span>
          </li>
        </ul>
      </li>
    </ul>
    <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
      <ul>
        <li v-for="(item,index) in shortcutList" :key="item" class="item" :data-index="index" :class="{'current':currentIndex===index}">{{item}}</li>
      </ul>
    </div>
    <div class="list-fixed" v-show="fixedTitle" ref="fixed">
      <h1 class="fixed-title">{{fixedTitle}}</h1>
    </div>
  </Scroll>
</template>

<script type="text/ecmascript-6">
import Scroll from '../scroll/scroll'
import Loading from '../loading/loading'
import { getData } from '@/assets/js/dom'

const TITLE_HEIGHT = 30
const ANCHOR_HEIGHT = 18

export default {
  props: {
    data: {
      type: Array,
      default: []
    }
  },
  computed: {
    shortcutList() {
      return this.data.map((group) => {
        return group.title.substr(0, 1)
      })
    },
    fixedTitle() {
      if (this.scrollY > 0) {
        return
      }
      return this.data[this.currentIndex]
        ? this.data[this.currentIndex].title
        : ''
    }
  },
  data() {
    return {
      scrollY: -1,
      currentIndex: 0,
      diff: -1
    }
  },
  methods: {
    refresh() {
      this.$refs.listview.refresh()
    },
    selectItem(item) {
      this.$emit('select', item)
    },
    onShortcutTouchStart(e) {
      let anchorIndex = parseInt(getData(e.target, 'index'))
      let firstTouch = e.touches[0]
      this.touch.y1 = firstTouch.pageY
      this.touch.anchorIndex = anchorIndex
      // this.currentIndex = anchorIndex
      this._scrollTo(anchorIndex)
    },
    onShortcutTouchMove(e) {
      let firstTouch = e.touches[0]
      this.touch.y2 = firstTouch.pageY
      let delta = ((this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT) | 0 //向下取整
      let anchorIndex = parseInt(this.touch.anchorIndex + delta)
      this._scrollTo(anchorIndex)
    },
    _scrollTo(index) {
      // console.log(index)
      if (!index && index !== 0) {
        return
      }
      if (index < 0) {
        index = 0
      } else if (index > this.listHeight.length - 2) {
        index = this.listHeight.length - 2
      }
      const topHeight = -this.listHeight[index]
      this.scrollY = topHeight
      this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
    },
    scroll(pos) {
      // 获取滚动的y轴距离
      this.scrollY = pos.y
    },
    // 计算每个group的高度
    _calculateHeight() {
      // 重置高度
      this.listHeight = []
      const list = this.$refs.listGroup
      // 一开始高度为0
      let height = 0
      this.listHeight.push(height)
      for (let i = 0; i < list.length; i++) {
        // 获取每个元素
        let item = list[i]
        height += item.clientHeight
        this.listHeight.push(height)
      }
    }
  },
  watch: {
    data() {
      // 数据变化到dom变化会有延时
      setTimeout(() => {
        this._calculateHeight()
      }, 20)
    },
    scrollY(newY) {
      // console.log(newY)
      const listHeight = this.listHeight
      // 当滚动到顶部newy>0
      if (newY > 0) {
        this.currentIndex = 0
        return
      }
      // 在中间部分滚动
      for (let i = 0; i < listHeight.length - 1; i++) {
        let height1 = listHeight[i]
        let height2 = listHeight[i + 1]
        // 最后一个，  向下滚动时，y为负
        if (-newY >= height1 && -newY < height2) {
          this.currentIndex = i
          this.diff = height2 + newY
          return
        }
      }
      // 当滚动到底部，且-newY>最后一个元素的上限
      // -2是因为，有上限和下限，所以会比列表多一个
      this.currentIndex = listHeight.length - 2
    },
    diff(newVal) {
      // console.log(newVal)
      // 只有小于一个标题的高度的时候，才会真正获取偏移量，也就是下一个group离顶部的高度
      let fixedTop =
        newVal > 0 && newVal < TITLE_HEIGHT ? newVal - TITLE_HEIGHT : 0
      if (this.fixedTop === fixedTop) {
        return
      }
      this.fixedTop = fixedTop
      this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
      // console.log('偏移了')
    }
  },
  created() {
    ;(this.touch = {}), (this.listenScroll = true), (this.listHeight = [])
  },
  mounted() {},
  components: {
    Scroll,
    Loading
  }
}
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
@import '~@/assets/stylus/variable';

.listview {
  position: relative;
  width: 100%;
  height: 100%;
  overflow: hidden;
  background: $color-background;

  .list-group {
    padding-bottom: 30px;

    .list-group-title {
      height: 30px;
      line-height: 30px;
      padding-left: 20px;
      font-size: $font-size-small;
      color: $color-text-l;
      background: $color-highlight-background;
    }

    .list-group-item {
      display: flex;
      align-items: center;
      padding: 20px 0 0 30px;

      .avatar {
        width: 50px;
        height: 50px;
        border-radius: 50%;
      }

      .name {
        margin-left: 20px;
        color: $color-text-l;
        font-size: $font-size-medium;
      }
    }
  }

  .list-shortcut {
    position: absolute;
    z-index: 30;
    right: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 20px;
    padding: 20px 0;
    border-radius: 10px;
    text-align: center;
    background: $color-background-d;
    font-family: Helvetica;

    .item {
      padding: 3px;
      line-height: 1;
      color: $color-text-l;
      font-size: $font-size-small;

      &.current {
        color: $color-theme;
      }
    }
  }

  .list-fixed {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;

    .fixed-title {
      height: 30px;
      line-height: 30px;
      padding-left: 20px;
      font-size: $font-size-small;
      color: $color-text-l;
      background: $color-highlight-background;
    }
  }

  .loading-container {
    position: absolute;
    width: 100%;
    top: 50%;
    transform: translateY(-50%);
  }
}
</style>
